[TeMPOraL]

Huge restrictions of available forms of marketing would be a good start. Done top-down, this levels the playing field, and reduces the advertising expenditure companies need to make - as most advertising costs go towards cancelling out equivalent spending from your competitors.

[tobltobs]

Introduction of a five-year plans for the national economy would cancel out all the spending from competitors.

[TeMPOraL]

I'm not thinking "five-year plans", I'm thinking GDPR + more restrictive laws on advertising content + ban on city billboards, ban on leaflets, + other regulations intent on heavily restricting all other forms of advertising.